1. Field of the Invention
The present invention relates generally to testing tools for testing blow-out preventors of a well, and more particularly, but not by way of limitation, to a testing tool for testing blow-out preventors of a subsea well.
2. Description of the Prior Art
Oil and gas wells typically have a blow-out preventor system located on top of the wellhead of the well. This blow-out preventor system will include several individual blow-out preventors of various types which are capable of closing in the well in the event excessive pressures are encountered downhole.
Particularly, when drilling a subsea well, governmental regulations generally require relatively frequent, e.g., weekly, testing of the blow-out preventors. The blow-out preventors of a subsea well are typically located at the ocean floor and thus may be several thousand feet below the drilling platform.
Also, in such subsea wells it is very typical that a tapered drill string is being used. The term tapered drill string refers to a system which utilizes a larger diameter drill string for drilling an initial portion of the well, and a smaller diameter drill string for drilling a lower portion of the well. For example, a typical tapered drill string might involve the use of both 5-inch outside diameter drill pipe and 31/2-inch outside diameter drill pipe.
The blow-out preventor system of such a subsea well must be capable of sealing off the annular space surrounding either the smaller or the larger drill pipe which may be used.
Testing of the blow-out preventor systems has typically been conducted through the use of a length of drill pipe of the diameter to be tested, with a test plug connected to the bottom of that drill pipe. The drill pipe and test plug are run into the well, and the blow-out preventor system is tested for that particular drill pipe size.
If it is desired to test the blow-out preventor against a second size of drill pipe, a second similar testing string is made up. The first string of pipe must be retrieved from the well, then the second testing string is run into the well.
This tripping of the test string out of the well between the tests on the two different sizes of drill pipe involves substantial time and expense on a subsea well, where as mentioned the wellhead may be located several thousand feet below the drilling platform.